[Elecraft] K3s Line Out (stereo)

[K9MA]

The headphone outputs from my radios are switched with some relays. The 
switching system has a common ground, which creates a ground loop, 
resulting in 60 Hz hum in the headphones. (Call it common impedance 
coupling, if you prefer.) I should have isolated the headphone grounds, 
but a path of less resistance was to insert the isolation transformers. 
They are just common 600 Ohm transformers, like the ones in the K3 line 
outputs, but they're a bit lossy driving headphones.

73,
Scott K9MA

On 1/16/2019 09:02, Bob McGraw K4TAX wrote:
> I see no need for isolation transformers with headphones.  Likely the 
> transformers is the reason the HP output won't drive a pair of 
> headphones.   Isolation transformers?  Are they 3 winding hybrid 
> transformers?    I've used them in professional audio installations 
> but they are rare and expensive.
>
> 73
>
> Bob, K4TAX
>
>
>>
>> On 1/15/2019 11:23 PM, K9MA wrote:
>>> I found that the level at headphone output, at least the rear panel 
>>> one, was too low to drive two pairs of headphones in parallel in my 
>>> setup, which includes some isolation transformers. The speaker 
>>> output works fine with the headphones. (Don't try this with super 
>>> sensitive low impedance headphones.) I just wired a switch to an 
>>> external speaker.
>>>
>>> 73,
>>> Scott K9MA
>>>
>>> On 1/15/2019 20:51, Nr4c wrote:
>>>> Why use Line Out for speakers. There is a perfectly good jack 
>>>> marked Speakers right next to the Phones jack. Be sure and use a 
>>>> Stereo plug but it is for ........wait for it.  Speakers!
>>>
>>>

-- 
Scott  K9MA

k9ma at sdellington.us